Ablation behavior experimentation on the hindbrain auditory system has led to the conclusion that the superior olivary complex (or SOC) in the medulla may serve the auditory system as an "acoustic chiasm". The primary evidence is that unilateral lesions in the auditory pathway anywhere below this structure (that is, in the cochlea, cochlear nucleus, trapezoid body) result in sound localization deficits either in both hemifields of auditory space of in the hemifield ipsilateral tot he lesion. In sharp contrast, unilateral lesions in the pathway anywhere above the SOC (that is, in the lateral lemniscus or beyond) result in sound localization deficits only in the hemifield contralateral to the lesion. Therefore, there is a clear functional parallel between the SOC and the optic chiasm even though there is no obvious anatomical parallel. We propose to continue studying the anatomical basis and functional consequences of this chiasm-like process in a series of tract-tracing, 2-DG, transmitter-identification, and ablation-behavior experiments in cats. In the new project period we will focus much of our early effort on the afferent supply and integrative activity of MSO and the relationship of its efferents to the ipsilateral efferent projections of LSO. Because the project entails rigorous psychophysical tests of sound localization acuity and basic hearing capacities before and affter selective hindbrain tract-sections, we hope the research will contribute to the understanding of retrocochlear dysfunction in humans.